Preparative layer

In the eadiest known paintings, the primitive cave paintings, paint was appHed directly onto the cave wall, with tittle or no preparation. As early as the Old Kingdom in ancient Egypt, however, wall surfaces were specially prepared using a coating of plaster. In time, the refinement and complexity of the preparation layers increased until in the Renaissance several layers of different composition and fineness were superimposed. Other preparations used, especially in the Far East, consisted of a clay layer. 

The medium is the binder which provides for the adhesion of pigments. The most important types are the temper media (glue, egg, and gum), the oils, and wax. In addition, for wall painting there is the tme fresco technique, where the pigments are laid down in a fresh, wet plaster preparation layer. Several other media have been used, but much less frequendy, eg, casein temper. In modem paints, a number of synthetic resins are used for this purpose. Contemporary artist paints are often based on acryhc polymers (see Acrylic ester polymers Paints). 

Methyl-1-phenylisoquinoline 2-oxide (l.OOg, 4.3 mmol) in acetone (200 mL) was irradiated with a Hanovia Q-700 medium-pressure Hg lamp until TLC showed that all starting material had been consumed. The solution was evaporated in vacuo, and the oily residue purified by preparative layer chromatography yield 0.485 g (48.5%) mp 73-75 C. 

Srnova-Sloutfova et al. [136] prepared layered Ag-core/ Au-shell bimetallic nanoparticles by overdeposition of Au... 

Manufacturers of TLC materials and accessories are well prepared to satisfy the needs for professionally performed PLC. High-quality precoated preparative plates are available from a number of eommercial sources. Alternatively, less expensive or specialty preparative plates ean be homemade in the laboratory, and loose sorbents and coating devices ean be purehased for this purpose. More-or-less-automated devices can also be purehased for band application of higher quantities of sample solutions to preparative layers. At least for some users, sophisticated densitometric and other instrumental techniques are available as nondestructive tools for preliminary detention and identification of separated compounds in order to enhance the effieiency of their isolation. The only aid still missing, and maybe the most important of all, is a comprehensive monograph on PLC that might encourage and instruct many potential users on how to fully benefit from this very versatile, efficient, relatively inexpensive, and rather easy to use isolation and purification technique. This book was planned to fill that void. 

Chapter 4 discusses the selection and optimization of mobile phases for successful separations in PLC. Chapter 5 details procedures for sample application and development of layers, and Chapter 6 complements Chapter 5 by dealing specifically with the use of horizontal chambers for the development of preparative layers, including linear, continuous, two-dimensional, gradient, circular, and anticircular modes. 

PREPARATIVE LAYER CHROMATOGRAPHY AS A PRACTICAL USAGE OF THE NONLINEAR REGION... 

With a growing implementation of the thin-layer chromatographic laboratories with densitometric scanners and particularly in the case of PLC, it seems quite important to reconsider definition of the Rp coefficient and the ways of its determination. Further, it seems strongly advisable to recommend the retardation factor in its i P(max) form as a more practical one for the preparative layer chromatographic usage. 

Modem planar chromatography is suitable not only for qualitative and quantitative analysis but also for preparative purposes. The separation efficiency of a thin-layer chromatographic system is independent of this intended purpose and is mainly determined by the quahty of the stationary phase, that is to say, by the applied coated layer. Therefore, progress in modem planar chromatography can be attributed not only to the development of the efficiency of the instmments but also to a large extent to the availability of high-quahty precoated layers. And today, as in the past, bulk sorbents for self production, especially of preparative layer chromatography (PLC) layers, are widely used. 

Planar chromatography has been used for preparative purposes in the past and is still used today. The reasons for the usage of preparative layer chromatography are, first of all, its cost-effectiveness and flexibility. 

Until now the application of different types of bnlk sorbents nsed for handmade PLC plates is rather widespread, and in most cases the mannfactnrers of these materials provide detailed instructions for the preparation of the preparative layers. However, the quality and especially the reproducibility of these handmade plates is frequently rather poor. Dne to this, the development of modem TLC and HPTLC, and precoated PLC plates also, becomes increasingly more important. 

From Nyiredy, Sz., Preparative layer chromatography, in Handbook of Thin-Layer Chromatography, 3rd ed., revised and expanded. Chromatographic Science Series, 89, Sherma, J. and Fried, B., Eds., Marcel Dekker, New York, 2003, chap. 11. 

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